DE102007016369A1 - Method for determining the blade pitch on wheels in integral design - Google Patents

Abstract

To detect mis-tunings of integral bladed wheels (BLISKs) based on the identification of blade natural frequencies, the individual blades are excited independently of each other, measuring the vibration response to calculate the actual blade pitch and detuning. During the measurement process, the unvisited blades are additionally detuned by means of a temporarily attached, respectively identical additional mass, so that the measurement of the vibration response of the excited blade disturbing coupling effects are shifted from the natural frequency near the blade and thereby eliminated.

Description

The The invention relates to a method for determining the blade pitch in integrally manufactured wheels for Compressors and turbines, especially for gas turbine engines, at the individual blades successively in each of the other Shovels largely decoupled state by means of pulse excitation excited and thereby the vibration response of the relevant blade is measured.

In the compressor and turbine technology and especially in aircraft engines are increasingly made in one piece wheels, so called BLISKs. Compared to the conventional Construction let the one-piece trained wheels higher rotational speeds, so that an improved Pressure ratio can be achieved and thus more powerful Engines are available. Wheels made in integral construction are increasingly also outside of aviation technology Compressors and turbines used. Because of the one-piece Training, however, are production-related disorders of Rotational symmetry, that is a detuning of the overall structure to record. This also known as "Mistuning" Special feature of wheels in BLISK construction, which is reflected in specific blade natural frequencies is due aerodynamic excitations with amplitude amplitudes and voltage peaks in the blades and consequent, the life of the Impeller limiting fatigue connected. Through a - realistic as possible - determination the Schaufeleigenfrequenzen it is therefore possible production-related Disruption of the rotational symmetry of the impeller, that is Tuning (Mistuning) of the forest, to recognize and appropriate Statements about the quality of the BLISK concerned with regard to their vibration behavior under operating conditions as well as their operational safety and service life.

In the US Pat. No. 7,082,371 B2 A method for determining the mistuning of rotating blade structures and, in particular, for predicting the vibration behavior of integrally constructed impellers (BLISKs) of gas turbines is described. Software can describe BLISK's normal modes and eigenfrequencies, using tuned system frequencies and frequency tuning of each blade / disk sector. In this known under the designation FFM (Fundamental Mistuning Model) methods are used for the determination of sector frequencies as well as tuned system frequencies normal, that is, non-tuned modes and natural frequencies of the relevant BLISK. The FMM method can predict how much the BLISK will vibrate during rotation under operating conditions. The method includes obtaining nominal frequencies of a tuned BLISK system, measuring at least one unmatched waveform, and calculating the mistuning of at least one blade of the BLISK from the desired frequencies and the at least one unmatched waveform and the natural frequency. The variables required for the calculation can advantageously be determined on a freely stored, unchanged system. However, the FFM method is only suitable for highly coupled systems with a low blade number. With a high number of blades occur within a frequency band of a few Hertz according to the number of blades eigenmode, which preclude a sufficiently ge precise fashion separation or must be separated with extremely complex methods.

In another known method for detecting the detuning of BLISKs or for predicting the blade vibrations of a BLISK during operation ( Sever, IA: Experimental Validation of Turbomachinery Blade Vibration Predictions, PhD thesis, University of London (Imperial College), 2004 ), the disc between massive steel blocks and additionally also the currently unmeasured blades are clamped with considerable effort in order to reduce the coupling effects between the blades during excitation and vibration measurement and in fact to be able to measure the natural frequency of the relevant blade. According to yet another investigation on the strength design of blade disks ( Beirow, B. u. a: Experimental and numerical investigations regarding a strength design optimization of high-pressure compressor blade disks with special consideration of mistuning effects, DGLR Congress 2003, Munich 2003, ISSN 0700-4083 ), only the disc is clamped and the individual blades of the BLISK are excited in succession by means of pulse excitation and simultaneously the vibration response is measured without contact. In this way it is possible in principle for completely or partially decoupled wheels in BLISK construction to relatively well identify relative shunting tunings to BLISKs. However, unambiguous vibration responses corresponding to the actual conditions during operation can not be achieved due to incomplete decoupling. Apart from the fact that the bracing requires considerable effort, the application of the aforementioned method is also limited to wheels, which can actually be braced, which is not always guaranteed due to the Bliskgeometrie, for example at a high number of blades, or built-in wheels ,

Of the Invention is based on the object, a method of the initially mentioned type for determining the blade pitch of Specify in BLISK design trained wheels, the regardless of the wheel design and also in the installed state the impeller with little effort sufficient decoupling the examined blade from the disc and the rest Shovels ensure and thereby a clear, realistic Vibration response of each excited blade and ultimately one clear statement about the blade natural frequency distribution and thus allows the impeller detuning.

According to the invention the task with a method according to the features of claim 1. From the dependent claims arise further features and advantageous developments of Invention.

Of the The basic idea of the invention, in other words, is that in a process under the Convention of Claim 1 during the measurement of the vibration response at the respectively excited shovel all others - straight not examined - blades of integral construction manufactured impeller with the help of a temporarily each unexamined bucket attached, identical additional mass additionally be upset. This will change the oscillation frequency of unexamined blades from the natural frequency range the blades shifted so that the vibrational response of the investigated Shovel disturbing and distorting coupling effects be substantially prevented. The natural frequency of the individual Shovels and thus the blade natural frequency distribution on the impeller and the detuning of the overall structure can thus be realistic be determined. With the production-related inevitable Mistuning Connected amplitude and voltage increases during operation can be detected in advance, so that reliable Statements on the fatigue problem and service life as well on the operational safety of BLISK.

According to one in claim 2 reproduced further important feature of the invention is to achieve the additional blade detuning one certain additional mass required, their size from the design shovel measures, the design blade frequency of the bucket modes and the expected magnitude of the blade pitch depends.

In Another embodiment of the invention are from the measured vibration response signals for each vane and mode family determines transfer functions, from which the maximum frequencies associated with the respective amplitude maxima be read out. From these an average value is calculated, finally, as a reference for presentation the blade natural frequency distribution or the detuning of the impeller serves.

In Advantageous development of the invention according to claim 4 it is possible to calculate the slightly too small Averages using a mass-spring-damper model as equivalent impeller model depending to correct for the blade rigidity and design blade mass.

In Embodiment of the invention are the additional masses as small metal cylinder formed, with the help of beeswax respectively at matching Positions are held on the blades not examined. The shock pulse The blade excitation is in each case at the same place and at the same angle generated by means of miniature hammer.

The Vibration response of the excited blade becomes non-contact detected by laser vibrometry.

The Application of the method is carried out in BLISK construction Compressor and turbine wheels, especially in compressor wheels of aircraft gas turbines, and in a well-developed state with virtually free Storage of the impeller or even when installed.

One Embodiment of the invention will be with reference to the drawing explained in more detail. Show it:

1 a schematic representation of an arrangement for determining the blade pitch in a trained as BLISK impeller of the high pressure compressor of an aircraft gas turbine;

2 a graph a) of a transfer function with the maximum amplitude for a part of the blades of the impeller and b) another representation of the transfer function for a single blade with the maximum frequency related to the maximum amplitude of a blade, and that is not sufficient in the prior art decoupled BLISK;

3 a graphic representation of the transfer functions after 2 , but in accordance with the invention using additional masses decoupled blades for unambiguous identification of the respective blade natural frequency;

4 an Equivalent Blisk Model (ÄBM) for the optional calculation of the frequency mean value correction; and

5 a block diagram for the iterative correction of metrologically determined blade fre quenzverteilungen.

As 1 shows is to be examined, trained in blisk design impeller 1 on a foam pad 2 stored virtually free. The impeller 1 includes a disc 3 with integrally formed on its outer periphery blades 4 , Apart from the just examined blade 4.1 are on all the rest of the blades 4 in each case in the same place, here in the area of the blade tip 5 and the blade leading edge 6 , given, identical additional masses 7 attached in the form of small metal cylinders. The respective additional mass 7 is held on a front side of the metal cylinder by means of an easily removable adhesive, here beeswax, on a side surface of the blade. The currently examined blade 4.1 is with a to a control unit 8th connected impact mechanism, here in the form of a pulse hammers 9 , energized by a miniature hammer blow impulse. The vibration response of the relevant blade 4.1 is from a measuring device, here one with the control unit 8th connected single-point laser vibrometer 10 , detected without contact by means of laser Doppler vibrometry. Because of with the help of additional masses 7 caused additional detuning of the remaining blades 4 are pushed out of these due to the pronounced in a BLISK blade-disc coupling, interfering coupling effects from lying in the vicinity of the measured blade natural frequency frequency range of interest, so that the detuning of the blade currently being examined 4.1 can be determined on the basis of the determined blade natural frequency. In the same way - each without additional mass 7 - then the remaining blades 4 examined. The impact pulse is always in the same place and at the same angle and in the same size on the particular blade to be examined 4.1 exercised.

The amount of additional mass Δm (g) becomes dependent on the design blade mass m _b (g), the design blade natural frequency of the i-th blade mode f _{0, i} (Hz), and the expected order of blade pitch, that is, the contributory mistuning range of the ith Blade mode Δf _span = Δf _max + Δf _min (%) where Δf _max = (f _{i, max} -f _{0, i} ) / f _{i, max} (%) is the maximum positive value of the mistuning and Δf _min = (f _{i, min} - f _{0, i} ) / f _{i, min} (%) are the negative minimum values of the mistuning of the i-th blade mode, respectively, and are calculated

This is an on-the-safe estimate because the effectively resonating blade mass assumes a smaller value compared to the actual design blade mass m _b .

From the force input signals and the vibration response signals, a transfer function is now calculated for each of the 80 blades of the BLISK 11 of a high-pressure compressor and each family of products (1st bend, 2nd bend, 1st torsor, 2nd torsor, etc.). The amplitude maxima occurring in the transfer functions H [m / s / N], in each case isolated due to the decoupling of the blade just measured from the other blades provided with additional masses (in US Pat. 3b ) Associated with the maximum frequencies f _i are as input variable for the relative blade natural frequency distribution (f _i - f _{i, medium)} / f _{i, medium)} ( 3b ) used. With the blade natural frequency distribution of the BLISK determined in this way for all fashion families, a reliable statement can be made about the blade pitch or the vibration behavior of the blades during operation and ultimately about the quality and service life of the BLISK.

2a To illustrate the disadvantages of the prior art shows the transfer function of the vibration responses of BLISK blades on the basis of metrologically determined transfer functions. The representation of a transfer function H [m / s / N] for the amplitude maximum of a single blade (no. 20) in 2 B makes clear that the blade natural frequency is not clearly identifiable due to coupling effects and therefore a reliable assessment of the BLISK is not possible. By contrast, the blade natural frequency is using additional masses 7 due to one of the respective amplitude maximum ( 3a ) associated with the single maximum frequency ( 3b ) clearly identifiable with the bucket No. 20. The blade frequency distributions determined by the method described above can be used for the adjustment of a finite element model and thus for the computation of forced oscillation responses, which ultimately provide the relevant information for an optimal strain gauge positioning.

Since the average values f _{i, mean} calculated above for the representation of the related vane frequency distribution are calculated to be too small due to unavoidable couplings and the additional masses used, the blade eigenvoltage distribution can be corrected by correcting the mean value using a mass-spring-damper model (FIG. Beirow, B. et al. Localization phenomenon in high-pressure compressor blade disks, VDI reports No. 168, 2006, ISBN 3-18-091968-X ) are reproduced in more detail. Such an equivalent Blisk model (ÄBM) is in 4 played. The information necessary for the correction is obtained by means of a numerical experiment. For this purpose, the metrology-determined frequency distribution is given to the model via an adaptation of the blade stiffnesses k _{b, i,} which is automated, for example, in a FORTRAN code _, and the pulse excitation from the measurement is simulated. The distribution determined with the aid of a time step integration method will lie on average below the measurement specification, so that an iterative increase in the blade stiffness in accordance with 5 until the metrologically determined frequencies have been reached. The in 5 illustrated iteration process can be done to reduce the computing time punctually on one or a few blades.

die gleichzeitig der Modellvorgabe des letzten Iterationsschrittes entspricht. Mit der so ermittelten absoluten Schaufeleigenfrequenzverteilung ist die Schaufelverstimmung hinreichend genau beschrieben.The distribution of the blade stiffnesses k _{b, i} adapted in this way, together with the known design blade mass m _{b ,} defines the blade natural frequency distribution of the BLISK with respect to the family of modes investigated

which simultaneously corresponds to the model specification of the last iteration step. With the thus determined absolute blade natural frequency distribution, the blade pitch is described with sufficient accuracy.

1

Wheel

2

Foam pad

3

disc

4

shovel with additional mass

4.1

shovel without additional mass

5

blade tip

6

Blade leading edge

7

additional mass

8th

control unit

9

Electronic hammer

10

Single-point laser vibrometer

Dm

size the additional mass

_b

Design blade mass

f _{0, i}

Design blade natural frequency

Δf _span

expected scoop upset

f _{i, max}

positive Maximum value of mistuning

f _{i, min}

negative Minimum value of mistuning

kb _{, i}

scoop stiffness

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - US 7082371 B2 [0003]

Cited non-patent literature

• - Sever, IA: Experimental Validation of Turbomachinery Blade Vibration Predictions, PhD thesis, University of London (Imperial College), 2004 [0004]
• - Beirow, B. u. a: Experimental and numerical investigations regarding a strength design optimization of high-pressure compressor blade disks with special consideration of mistuning effects, DGLR Congress 2003, Munich 2003, ISSN 0700-4083 [0004]
• - Beirow, B. et al. Localization phenomenon in high-pressure compressor blade disks, VDI reports No. 168, 2006, ISBN 3-18-091968-X [0025]

Claims (10)

A method for determining the blade pitch in integrally manufactured impellers for compressors and turbines, in particular for gas turbine engines, wherein the individual blades successively excited in each of the remaining blades largely decoupled state by a pulse and thereby the vibration response of the energized blade as the output value for calculating the Detuning is measured, characterized in that the unexamined blades are additionally detuned by means of a temporarily attached to this, each identical additional mass that of these outgoing, the measurement of the vibration response of the blade examined interfering coupling effects shifted from the shovel frequency near frequency range and thereby eliminated , A method according to claim 1, characterized in that the size of the additional mass (• m) as a function of the design blade mass (m _b ), the design blade natural frequency of the i-th blade mode (f _{0, i} ) as well as the expected magnitude of blade disbalance (• f _span ) corresponding

is determined. Method according to Claim 1, characterized in that the transmission frequencies determined by measurement for each blade and mode family are determined by the maximum frequencies (fi) assigned to the corresponding amplitude maxima and as input variables for the relative blade frequency distribution (f _i -f _{i, medium} ) / f _{i, mean} ) of the impeller. Method according to Claim 3, in which the average values (f _{i, middle} ) calculated to be too small for establishing the blade frequency distribution are corrected by means of an equivalent blisk model (ÄBM) mass-spring-damper model, wherein the metrologically determined frequency distribution corresponds to the equivalent blisk model via an automated adjustment of the blade stiffnesses (k _{b, i} ) and simulating the pulse excitation from the measurement, and wherein the absolute blade natural frequency distribution for determining the blade pitch of the BLISK as a function of the blade stiffnesses (k _{b, i} ) and the design mass ( m _b ) out

results. Method according to claim 1, characterized in that that the additional masses are designed as small metal cylinders, each at the same place with the help of an adhesive to the not examined blades are held. Method according to claim 5, characterized in that that a beeswax is used as the adhesive. Method according to claim 1, characterized in that that the blade excitation via a miniature hammer impact pulse takes place and the vibration response contactless means Laser Doppler Vibrometry is detected. Method according to claim 7, characterized in that that the impact pulse on the blades each in the same place and at the same angle. Method according to claim 1, characterized in that that the wheel to be examined in a dismantled state virtually free is stored. Method according to claim 1, characterized in that that the impeller in question is examined in the installed state.